CN112823467A

CN112823467A - Stator tooth, associated yoke and stator for an electric machine

Info

Publication number: CN112823467A
Application number: CN201980066519.0A
Authority: CN
Inventors: O·贝斯巴德; T·劳伦; M·拉乌尔
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2018-10-16
Filing date: 2019-09-23
Publication date: 2021-05-18
Also published as: FR3087304B1; FR3087304A1; EP3868008A1; WO2020078667A1

Abstract

The invention relates to a stator tooth for an electrical machine, comprising a wrapper (12) extending between a first face (13) having means for fixing to a stator yoke and an opposite second face (14). The envelope contains one or more electrically conductive materials configured to direct magnetic flux of the electric machine from one of the faces to the other face in operation.

Description

Stator tooth, associated yoke and stator for an electric machine

Technical Field

The present invention relates to an electric rotating machine, in particular for an electric or hybrid motor vehicle.

More particularly, the present invention relates to a stator including teeth attached to a stator yoke.

Background

Rotating electrical machines generate losses in the form of heat, especially caused by eddy currents. In the part of such machines that conducts the magnetic flux, the magnetic field generates heating, because induced currents, called eddy currents, flow there in short-circuit circuits, and because they present a resistance to the flow of the magnetic flux. To prevent this, the conducting parts of the stator and rotor are almost systematically made up of a stack of lamellae, which are electrically insulated from one another and oriented in the direction of the magnetic field.

In a machine in which one or more rotors comprise permanent magnets, the magnetic properties of which depend on the temperature, the efficiency of the machine depends inter alia on the magnetization of the rotor or rotors.

In particular, if the temperature of the one or more rotors is above a critical temperature, the magnets irreversibly lose their magnetism. In addition, eddy currents flow in the magnets, thereby contributing to their heating.

Furthermore, the heat generated by the motor reduces the overall efficiency of the motor.

In a central rotor axial flux rotating machine, the rotor is arranged between two stators, the rotor and the stators dissipating heat.

Therefore, the rotor is heated by the induced current flowing therethrough and the heat radiated from the stator.

Document GB 2482928 discloses a central stator axial flux rotating electrical machine, that is to say an electrical machine in which the stator is arranged between two rotors comprising magnets.

Since the rotors are arranged at the ends of the electrical machine, they are cooled by the cold air.

This document also discloses that the central stator comprises discs made of composite plastic material, supporting stator pads made of compressed and sintered iron powder, the particles of which are coated with an electrically insulating material, which reduces the resistance of the supporting stator pads to the magnetic flux passing through them.

Therefore, the induced current causing the heating of the stator is reduced therein.

However, the magnetic loss of the rotor is increased by the magnetic flux leaving circulation through the support plate for the magnet.

Reference may also be made to document FR 3006124 which discloses a central rotor axial flux rotating electrical machine.

The rotor includes a disk including openings arranged in a circumferential direction and receiving magnets.

This configuration allows limiting the heating of the rotor.

However, the heat radiated from the stator causes the stator to be heated.

It is proposed to overcome the drawbacks associated with the rotating electrical machines according to the prior art, in particular by limiting the heating of one or more stators surrounding the rotor.

Disclosure of Invention

In view of the above, one subject of the present invention is a stator tooth for an electrical machine, comprising a wrapper extending between a first face comprising means for attachment to a stator yoke and an opposite second face.

The envelope contains one or more electrically conductive materials configured to direct magnetic flux of the electric machine from one of the faces to the other in operation.

Preferably, the envelope is made of a stamped non-magnetic sheet metal.

Advantageously, the first face comprises at least one tab intended to be attached to the yoke.

According to another feature, the second face comprises at least one tab for fixing, in the axial direction, the pre-assembled winding interposed between the tab and the tab.

Preferably, the tooth further comprises a pre-assembled winding inserted on the outer circumferential surface of the envelope.

Advantageously, the pre-assembled winding comprises a support frame on which a wire is wound, the wire comprising a plurality of strands held in an insulating envelope to form turns.

According to a first embodiment, the electrically conductive material comprises pins extending from the first face to the second face.

Preferably, the needles are made of a material that is permeable to magnetic fields and has grains oriented along the length of the needles.

Advantageously, the peripheral surface of each needle not delimited by the first face and the second face is covered with an insulating material.

Preferably, the gap between the needles and the envelope is filled with an adhesive.

According to a second embodiment, the electrically conductive material comprises sheets extending from the first side to the second side and stacked on top of each other.

Preferably, the gap between the sheets and the envelope is filled with adhesive.

According to a third embodiment, the tooth comprises a one-piece pad, the electrically conductive material being made by compacting iron powder coated with an electrical insulator.

Preferably, the electrically conductive material further comprises lateral extensions extending outwardly from the envelope and comprising recesses for receiving clips attached to the yoke.

Further subject matter of the invention is a yoke comprising at least one stator tooth as defined above, a stator for a central rotor electrical machine comprising such a yoke, and a central rotor axial flux electrical machine comprising such a stator.

Drawings

Other objects, features and advantages of the present invention will become apparent from a reading of the following description, given purely by way of non-limiting example and with reference to the accompanying drawings, in which:

figure 1 illustrates a cross-sectional view of a central rotor axial flux rotating electrical machine according to the present invention;

figure 2 shows a view of a yoke and stator teeth according to the invention;

figures 3 and 4 illustrate a first embodiment of a stator tooth according to the invention;

figure 5 illustrates a second embodiment of a stator tooth according to the invention; and is

Figure 6 illustrates a third embodiment of a tooth formed by a stator pad according to the invention.

Detailed Description

Referring to fig. 1, a cross-sectional view of a center rotor axial flux rotating electrical machine 1 in an axial direction is shown. In this exemplary embodiment of the invention, the machine is a traction motor for an electric or hybrid vehicle.

The electric machine 1 comprises a housing 2 comprising two

stators

3a and 3b of the same architecture, which surround the rotor 4, and an axis (a) coinciding with the rotation axis of the rotor 4.

Each

stator

3a and 3b is separated from the rotor by an air gap ENT.

The rotor 4 is guided by

ball bearings

5 and 6 supported by the housing 2.

The rotor 4 comprises a hub 7 to which a disk 8 is attached, which disk comprises openings arranged circumferentially and housing magnets 9, which are preferably segmented and electrically insulated to limit the currents induced in the magnets.

Thus reducing the heating of the rotor 4.

The disc is preferably made of a composite material, for example a fibre-reinforced polymer, thus reducing eddy currents. The disc is preferably surrounded by a hoop to improve its mechanical strength.

The rotor 4 is positioned axially between the

stators

3a and 3b to obtain an air gap of equal thickness. For this purpose, an adjustment is provided on one side (for example on the right). Measurements were made to determine the thickness of the piece. To hold the rotor in this position, a spring is placed behind the bearing opposite the piece.

The stators are each centred in the two half-shells and are kept axially compressed by means of pin-joint means welded to the yoke 10 and nuts regularly and circumferentially distributed around the yoke 10.

In order to cool the

stators

3a and 3b, a water chamber is disposed in each housing. Sealing of these chambers is provided by O-rings.

Since the

stators

3a and 3b have the same architecture, only the stator 3a will be described in detail hereinafter.

The stator 3a comprises a yoke 10 around which stator teeth 11 are arranged, which stator teeth are all identical.

The yoke 10 has a constant thickness, and includes, for example, a thin sheet whose surface is electrically insulated and wound in a spiral shape and has a steel grain oriented in a winding direction. As a variant, the yoke is made of non-oriented steel grains. Thus, in operation, the magnetic flux that must flow between two adjacent teeth will follow the orientation given by the winding of the sheet. As a variant, a magnetically permeable material other than steel is used.

Fig. 2, 3 and 4 show views of the yoke 10 comprising a first preferred embodiment of the stator teeth 11, as well as a partial section through the yoke 10, and the stator teeth 11 in the direction III-III shown in fig. 2.

More particularly, refer to fig. 3.

The stator teeth 11 comprise a wrapper 12 extending between a first face 13 attached to the yoke 10 and a second face 14. These faces are orthogonal to the axial direction (the rotational axis (a) of the rotor).

The envelope 12 contains one or more electrically conductive materials.

According to a first preferred embodiment, the conductive material comprises needles 15. The envelope 12 is for example an isosceles triangle whose vertices are rounded and whose sides of equal length are oriented so that the teeth are symmetrical with respect to the symmetry axis (B). The common vertex of two sides of the same length is oriented towards the axis (a).

The needles 15 extend from the first face 13 towards the second face 14. More precisely, the needle 15 extends in an axial direction. The length of the needle is preferably substantially equal to the axial dimension of the envelope 12, which is itself greater than the thickness of the yoke 10. The diameter of the needle (or the size of the cross-section in the case where the needle is not cylindrical) is preferably of the order of 0.5mm, and preferably less than 1 mm. It may be less than 0.5mm and depends on the frequency of use of the rotating electrical machine 1. For example, a diameter of less than 0.3mm is preferred at 1000 Hz.

The set of needles of the stator teeth 11 is substantially trapezoidal or triangular in axial section with rounded corners. The periphery of the envelope 12 forms a strip, the width of which extends in the axial direction between the

faces

13 and 14 and the length of which extends angularly all around the shape described by the needles of the stator teeth 11. However, the envelope 12 does comprise tabs 16 positioned on the surface of the yoke 10 orthogonal to the axis (a), perpendicularly to the strip formed by this perimeter of the envelope 12. Similarly, fins 22, positioned perpendicular to the strip formed by this perimeter, keep the windings 17 assembled around the strip.

The envelope 12 is made, for example, by stamping a non-magnetic metal sheet.

The needle 15 is, for example, cylindrical and is preferably made of a material permeable to magnetic fields and having grains oriented in its length direction, for example made of magnetic steel. Of course, the shape of the cross section of the needle may be different, for example polygonal.

The peripheral surface of each needle 15 not delimited by the first face 13 and the second face 14 is coated with an insulating material (not shown), for example varnish, so that the needle 15 is in magnetic contact with the yoke 10 and so that the magnetic field can be transferred from the yoke 10 to the rotor 4 via the needle 15 and the air gap ENT. In other words, the needles are preferably in direct contact with the yoke 10 without insulating material separating them.

The gap between the needle 15 and the envelope 12 is filled with an adhesive, such as a resin (not shown). In addition to having an adhesive function, the adhesive also has electrical insulating and thermal conducting properties.

The insulation of the needles 15 from each other and from the envelope 12 allows the induced current responsible for heating the stator 3a to be reduced.

The first face 13 includes tabs 16 attached to the yoke 10 to secure the teeth 11 to the yoke 10.

Each tab 16 is attached to the yoke 10, for example by laser welding through the tab. Preferably, three tabs 16 attach the needle-containing envelope to the yoke 10, one tab 16 being located at the radially outer periphery of the teeth 11 and two side tabs 16 being located on either side of the teeth 11 in the angular direction.

Stator teeth 11 further include a pre-assembled winding 17 inserted on the outer circumferential surface of envelope 12.

The pre-assembled winding 17 comprises a support frame 18 on which the wire 19 is wound, forming turns.

The wire 19 preferably includes a plurality of strands 20 held in an insulating jacket 21. For a given conductive cross section of the wire, the current flow is improved by using multiple strands as opposed to a one-piece wire.

The second face 14 of the envelope 12 comprises deformable tabs 22 which are pressed back to fix the pre-assembled winding 17 in the axial direction when the pre-assembled winding 17 is assembled on the tooth 11.

As seen in fig. 2, the teeth 11 are evenly arranged around the yoke 10.

The yoke 10 is circular and includes a void at its center that is sized to receive the rotor 4.

In operation, the magnetic field generated by the turns of the teeth 11 of the stator 3a passes through the air gap ENT and the disk-shaped portion of the rotor 4 and penetrates into the stator teeth arranged facing the stator 3 b.

The magnetic field is guided by the yoke of the stator 3b to the adjacent teeth and then passes through the air gap ENT and the disk-shaped portion of the rotor 4 again and penetrates into the stator teeth arranged facing the stator 3a, thus reaching the adjacent stator teeth via the yoke of the stator 3 a.

The needles 15 of the stator teeth 11 are oriented in the direction of travel of the magnetic field and the blades of the yoke 10 are wound in the direction of travel of the magnetic field.

The circulation of the magnetic flux is optimized, thus reducing the magnetic losses of the machine 1 and improving the efficiency of the machine 1.

Fig. 4 shows a partial view of the tooth 11 comprising the needle 15 housed in the envelope 12, and the tab 16.

According to a second embodiment of the tooth 11 illustrated in fig. 5, the conductive material comprises lamellae 23 stacked in a radial direction inside the envelope 12.

The thickness of the sheet 23 extends in the radial direction, the width of the sheet extends between the first face 13 and the second face 14, and the length of the sheet extends in a direction orthogonal to the radial direction.

The sheet 23 is, for example, rectangular in cross section.

The sheets 23 are stacked, for example, in a direction parallel to sides having different lengths with respect to the lengths of the other two sides of the isosceles triangle.

The lamellae 23 are fixed to each other, for example by means of surface welds, before being inserted into the envelope 12. After the foil 23 has been inserted into the envelope 12, the gap between the foil and the envelope is filled with an adhesive, for example a resin.

The thickness of the sheet is preferably less than 0.35mm, for example equal to 0.2 mm. The thickness is selected depending on the frequency of use of the rotating electric machine 1.

Fig. 6 shows a third embodiment of the tooth 11 attached to the yoke 10.

This tooth 11 comprises a pad and a tab 16.

In this embodiment, the pad is a one-piece pad and the conductive material is made by compacting iron powder coated with an electrical insulator.

The pad further comprises lateral extensions 24 extending towards the outside of the pad on both sides of the axis of symmetry (B) and comprising a recess 25 at each end of the extension. The lateral extension 24 forms an isthmus, thereby increasing the torque generated by the rotary electric machine 1.

Clips

26 and 27 made of resilient steel attached to the yoke 10 are received in the recess 25 to hold the pad against the yoke 10.

The tabs 22 clip over the

clips

26 and 27 and hold the pre-assembled winding 17 (not shown) on the peripheral surface of the envelope 12 by welding its ends to the yoke. More specifically, the tabs 22 ensure that the pad is pressed against the yoke 10 with a certain pressure via clips supported on the pad in the recesses 25. In this third embodiment, the tabs hold the pads and coils.

The steel grains of the iron powder are magnetically oriented in the axial direction.

The fine segmentation of the stator teeth 11 mounted on the yoke 10 makes it possible to prevent losses by eddy currents.

The present invention is not limited to embodiments with respect to a central rotor axial flux machine, and the features described can be readily converted to a radial flux machine. In this case, the stator yoke may be segmented to facilitate assembly of the teeth and windings of the stator.

Claims

1. A stator tooth for an electrical machine, the stator tooth comprising an envelope (12) extending between a first face (13) and an opposite second face (14), the first face comprising means for attachment to a stator yoke (10), characterized in that the envelope contains one or more electrically conductive materials permeable to magnetic fields and configured to direct the magnetic flux of the electrical machine from one of said faces to the other in operation, said tooth further comprising a pre-assembled winding inserted on an outer peripheral surface of the envelope (12), said envelope being distinct from a support frame for said pre-assembled winding.

2. A tooth in accordance with claim 1, wherein the envelope (12) is made of stamped non-magnetic sheet metal.

3. The tooth of any one of claims 1 and 2, wherein the first face (13) comprises at least one tab (16) intended to be attached to the yoke (10).

4. The tooth of claim 3, wherein the second face (14) comprises at least one tab (22) for fixing a preassembled winding (17) inserted between the tab (16) and the tab in an axial direction.

5. A tooth in accordance with claim 4, wherein the pre-assembled winding (17) comprises said support frame (18) on which is wound a wire (19) comprising a plurality of strands held in an insulating envelope to form turns.

6. The tooth of any of claims 1-5, wherein the conductive material comprises a pin (15) extending from the first face to the second face.

7. A tooth in accordance with claim 6, wherein the needles (15) are made of a material permeable to magnetic fields and having grains oriented along the length of the needles (15).

8. The tooth of any one of claims 6 and 7, wherein a peripheral surface of each needle (15) not bounded by the first face and the second face is covered with an insulating material.

9. The tooth of any of claims 6 to 8, wherein the gap between the needles (15) and the envelope (12) is filled with adhesive.

10. The tooth of any of claims 1 to 5, wherein the electrically conductive material comprises lamellae (23) extending from the first face (13) to the second face (14) and stacked on top of each other.

11. A tooth in accordance with claim 10, wherein the gap between the lamellae (23) and the envelope (12) is filled with adhesive.

12. The tooth of any of claims 1-5, wherein the tooth comprises a one-piece pad, the electrically conductive material being made by compacting iron powder coated with an electrical insulator.

13. The tooth of claim 12, wherein the conductive material further comprises lateral extensions (24) extending outwardly from the envelope and including recesses (25) for receiving clips (26, 27) that press the envelope against the yoke (10).

14. A stator yoke comprising at least one tooth as claimed in any preceding claim.

15. A stator for a central rotor axial flux electric machine, the stator comprising a yoke (10) as claimed in claim 14.

16. A central rotor axial flux electric machine comprising a stator as claimed in claim 15.